1. Field of Invention
The invention relates to mufflers for internal combustion engines and, more particularly, to a catalyst muffler system with improved capability for cooling the exhaust gas stream for an internal combustion engine used on portable tools such as air blowers, flexible line trimmers, edgers, chain saws, and the like.
2. Description of Related Art
Portable tools such as air blowers, flexible line trimmers, edgers, chain saws, and the like are commonly used and becoming more prevalent as people seek the convenience provided by such tools. It is widely appreciated that such tools can emit exhaust that increase air pollution. Typically the exhaust gas is energy rich, especially for small two-stroke engines, as complete burning of the fuel is not obtained. To curb the problem, regulations requiring increasingly low exhaust emission output levels have been passed.
It is known to use catalytic converters in a muffler for a small internal combustion engine used on portable tools to reduce noxious components of exhaust gas, such as hydrocarbons and carbon monoxide. An exothermal chemical conversion takes place in the catalytic converter where, for example, hydrocarbons are converted to carbon dioxide and water. The exhaust gas typically enters the muffler with a temperature of approximately 600 degrees centigrade (C.). Burning the unburnt hydrocarbons causes the temperature of the exhaust gas to increase in the catalytic converter 40 to about 1000 degrees C.
The high temperature of exhaust gas has several identifiable problems. With hand-held portable tools, operating personnel can be endangered by both high temperature exhaust gas and ignition of exhaust gas. The exhaust gas can ignite if it reaches ambient air containing oxygen, through the exhaust outlet or through a gap at a partition interface of the muffler housing, at temperatures high enough for ignition.
Accordingly, there is a need for a compact and light weight muffler for a small internal combustion engine having a relatively low exhaust emission output level and relatively low exhaust gas stream exit temperature and muffler housing surface temperature. Additionally, the muffler should provide good noise reduction, maintain good engine performance, and be reliable, inexpensive, and easy to manufacture.